1. Field of the Invention
The present invention relates to a method of observing a magnified image and, more particularly, to a method of observing a magnified image of a sample by the use of a transmission electron microscope.
2. Description of the Related Art
The transmission electron microscope is for focusing an electron beam transmitted through a sample interior, making it possible to observe an interior structure of the sample. With the transmission electron microscope, it is possible to observe lattice defects and grain-boundary structure of a material, precipitate size and distribution or lattice images.
Concerning a transmission electron beam image of a sample by the transmission electron microscope, the field of view is not always coincident at between low magnification and high magnification even at the same coordinate of position. This is because the transmission electron microscope image undergoes the effects of a hysteresis native to a lens, thermal drift on a sample and axis deviation caused upon magnification change and hence the field of view is moved in position by a change of observing magnification.
It is an object of the present invention to provide a method of observing a sample which can automatically correct a movement in view field caused upon changing a magnification, in view of the foregoing problem to be encountered in observing a sample magnified image by using a transmission electron microscope.
A method of observing a sample by a transmission electron microscope, for achieving the foregoing object, according to the present invention comprises: a step of inputting a first magnification for use in searching a field of view and a second magnification for use in recording; a step of setting a magnification of a transmission electron microscope to the first magnification; a step of imaging a transmission electron beam image of a sample held on a sample stage by imaging means and displaying the transmission electron beam image of the sample in the first magnification on an image display section; a step of computing and storing a sample stage coordinate of a subject of recording designated over the transmission electron beam image of the sample displayed on the image display section; a step of cutting an image of the subject of recording out of the transmission electron beam image of the sample in the first magnification and storing a cut-out image as a first image; a step of setting the magnification of the transmission electron microscope to the second magnification; a step of moving the sample stage to the stored sample stage coordinate of the subject of recording; a step of capturing the transmission electron beam image in the second magnification with the same number of pixels as the first image and storing a captured image as a second image; a step of computing a movement amount of between the two images from a correlation intensity of the first and second images; a step of correcting a position of the transmission electron beam image in the second magnification with respect to the imaging means such that the movement amount is zero; and a step of recording the transmission electron beam image in the second magnification imaged by the imaging means.
Herein it is preferred to further comprise a step of computing a size of a region on the sample to be recorded in the second magnification over the transmission electron beam image of the sample in the first magnification, and a step of displaying a mark representing a region in a computed size by being superposed over a corresponding area of the transmission electron beam image in the first magnification.
A method of observing a sample by a transmission electron microscope comprises: a step of inputting a first magnification for use in searching a field of view; a step of setting a magnification of a transmission electron microscope to the first magnification; a step of imaging a transmission electron beam image of a sample held on a sample stage by imaging means and displaying the transmission electron beam image in the first magnification on an image display section; a step of acquiring information concerning a recording region designated over the transmission electron beam image of the sample displayed on the image display section; a step of computing and storing a sample stage coordinate of the recording region and a second magnification capable of putting the recording region fully in a field of view from the acquired information; a step of cutting an image in the recording region out of the transmission electron beam image of the sample in the first magnification and storing a cut-out image as a first image; a step of setting the magnification of the transmission electron microscope to the second magnification; a step of moving the sample stage to the stored sample stage coordinate of the recording region; a step of capturing the transmission electron beam image in the second magnification with the same number of pixels as the first image and storing a captured image as a second image; a step of computing a movement amount of between the two images from a correlation intensity of the first and second images; a step of correcting a position of the transmission electron beam image in the second magnification with respect to the imaging means such that the movement amount is zero; and a step of recording the transmission electron beam image in the second magnification imaged by the imaging means.
It is possible to designate a recording region on the transmission electron beam image of the sample displayed on the image display section, for example, by clicking two diagonal points of a rectangular recording region with using a mouse or dragging a rectangular frame representing a recording region with using a mouse.
The transmission electron beam image in the second magnification with respect to the imaging means can be corrected in position by moving the sample stage or deflecting an electron beam transmitted through the sample with using a sample image moving coil.
It is preferred to further comprise a step of determining a movement amount of an image when an electron beam to be irradiated to the sample is inclined by a predetermined angle, and a step of correcting an objective current value on the basis of the movement amount of the image thereby correcting for focusing of an objective lens.
The movement amount between the two images may be displayed on the image display section.
The sample observing method of the invention has the following features:
1) a recording object can be coordinate-displayed on an image taken with a low magnification;
2) a recording region can be graphic-displayed on an image taken with a low magnification;
3) an observation field of view can be automatically corrected; and
4) a focus can be automatically corrected.